1. Field of the Invention
The present invention relates to a slimming method of a carbon-containing thin film such as a patterned resist film formed on an object to be processed such as a semiconductor wafer, and an oxidation apparatus.
2. Description of the Related Art
In general, various processes such as film-formation, etching, oxidation, diffusion, surface modification, and removing of a natural oxide film are performed on a semiconductor wafer that may be a silicon substrate or the like in order to manufacture a semiconductor integrated circuit. When the above processes are performed in a vertical, so-called a batch type thermal processing apparatus disclosed in Patent Reference 1, semiconductor wafers are transferred from a cassette that may hold a plurality of semiconductor wafers, for example, 25 of semiconductor wafers, to a vertical wafer boat, to be supported by the wafer boat in multiple layers. About 30 to 150 of wafers may be placed on the wafer boat, depending on, for example, a size of the wafer. The wafer boat is transferred (loaded) into a process chamber, which may be evacuated, from a lower portion of the process chamber, and inside the process chamber is sealed hermetically. In addition, a predetermined annealing process is performed while controlling various process conditions such as a flow rate of a process gas, a process pressure, and process temperature.
Here, accompanied with high integration of the semiconductor integrated circuit, line widths or gaps required by manufacturing processes are fine. In general, fine patterns forming the semiconductor integrated circuit are formed by a photolithography technology. For example, patterns of a resist film are formed on the semiconductor wafer by the photolithography technology, and a base film is etched by using the resist patterns as a mask to form fine patterns.
According to the photolithography technology, a liquid immersion exposure method that effectively reduces an exposure wavelength by disposing liquid such as water having a greater refractive index than that of air between a wafer and an exposure device in order to improve a resolution of the exposure device by using ArF laser beam having a short wavelength has been adopted in order to meet the demands for miniaturization. However, the recent demand of miniaturization has exceeded the limitation in resolution according to the photolithography technology.
Therefore, according to the recent demand of further miniaturization, a method of forming fine patterns, which combines a film-forming process for forming a silicon oxide film on a carbon-containing thin film such as a patterned resist film and a side wall transfer (SWT) process or a lithography-lithography etching (LLE) method, has been suggested recently (for example, Patent References 2 and 3).
According to the SWT process, a slimming process in which entire surfaces of protruded portions on the pattern formed of, for example, resist film, are appropriately oxidized to be removed, is performed in order to reduce widths of the protruded portions substantially. In addition, a silicon oxide film is formed on the resist pattern, and the silicon oxide film is appropriately etched-back such that side walls formed on side surfaces of the protruded portions remain. Then, the exposed resist pattern is removed so as to etch a base layer that is an etch target layer by using the remaining side walls as a mask, and thus, fine patterns that may overcome the limitation in resolution according to the photolithography technology may be obtained.
However, according to the slimming process that oxidizes and removes the surfaces of the protruded portions on the carbon-containing thin film such as the patterned resist film as described above, a plurality of objects to be processed are held in a batch type process chamber that is elongated in a longitudinal direction, and an oxidizing gas, for example, oxygen, flows into the process chamber to generate plasma in an oxygen atmosphere so that the surface of the carbon-containing thin film is appropriately oxidized by active oxygen species to trim the surface of the carbon-containing thin film.
However, in the above described slimming process, the slimming process depends on the number of wafers held in the process chamber at a time, or has an insufficient reproducibility due to an unevenness of a slimming amount (trimming amount) in each of the slimming processes.
Prior Art Reference
(Patent Reference 1) Japanese Patent Laid-open Publication No. 2010-161162
(Patent Reference 2) Japanese Patent Laid-open Publication No. 2004-080033
(Patent Reference 3) Japanese Patent Laid-open Publication No. 2010-103497